Here's an interesting question, I'd like an answer to. As stated in my 1st post re the good word, basilect, it has become my lot in life to proofread things. That said, and in a nutshell, I am currently proofreading the grammar for a book my boss (who also happens to be my mom) is writing. I feel more than a little small for this task. However, this question has come up between us several times.

Should it be: Love is a verb that is common in most sentences.OR: Love is a verb which is common in most sentences.

Which (ha ha) is correct? When is "that" the proper word to use or does it even matter?

Hmm... Context would help here. My initial instinct is to go for that, because it is introducing a restrictive relative clause. However, is love common to most sentences? However, if the sentence is telling us that love is a verb, and that verbs are common to most sentences, one should use a comma:

"Love is a verb, which is common to most sentences."

However, that sentence is misleading. The natural sentence would be:

"Love is a verb that is common to most sentences."

This tells us that most sentences have the verb love in them. This might not be factually true, but is grammatically correct.

The second form is not wrong, but is generally considered to be less correct.

Okay, I see your point. That sentence was not taken from the book's text, but from my head and may have been a poor example. Here are a couple of samples from the book. I have included extra sentences for context. Please keep in mind, I am not responsible for content.

1. In reverse manner, a problem relating to pride which challenges our life is a magnified sense of inadequacy. We can better understand this as we follow an example.

2. I remember an incident in my life which lifted anger and wrath to new heights.

3. The function of faith, hope and love is reminescent of the effectual operation of our air conditioning system. Our system is comprised of two units which work together. One unit is in our backyard and the other unit is in our attic. (FWIW, I have never liked the structure of the sentences in example #3.)

1. In reverse manner, a problem relating to pride which challenges our life is a magnified sense of inadequacy. We can better understand this as we follow an example.

2. I remember an incident in my life which lifted anger and wrath to new heights.

3. The function of faith, hope and love is reminescent of the effectual operation of our air conditioning system. Our system is comprised of two units which work together. One unit is in our backyard and the other unit is in our attic. (FWIW, I have never liked the structure of the sentences in example #3.) ...

I think, as both Garzo and the writers of the article on the englishplus.com site to which you provided a link seem to do, that the problem is not so much which of the two relative pronouns «that» or «which» should be used -

Some teachers also tell you that that should be used with restrictive modifiers and that which should be used with nonrestrictive modifiers. Historically, there is little evidence that this "rule" ever had a significant effect on English expression [emphasis added[sub]MHD[/sub]], but writers should be aware that some correspondents have been taught this practice.

- but rather how commas should be employed to distinguish restrictive from non-restrictive relative clauses. In the first sentence, if it is pride which is considered as «challeng[ing] our life [lives ?]», then a comma should be inserted after «pride» ; if it is, rather, «a problem relating [I should say «related»] to pride», which is the subject of the relative clause (I think this reading the more likely), no comma should be used. In the second sentence, I should not use a comma, as the information following the subject «incident in my life» is required for identification ; however, I should prefer to place a comma after «units» in the third sentence, as I don't regard the fact that they work together essential for identifying them. Someone who feels that this information is required for identifying the units - there might, in another case, be lots of units, only two of which work together - would punctuate differently. (My problems with the third sentence is more the use of «is comprised of» for «is composed of», but I'm old-fashioned.) Personally, I am not particularly sensitive to putative distinctions between «which» or «that» in cases like the above, but if I 'm not mistaken, the grammar check in Windows follows the «rule» mentioned above....

Suzanne, I think in each of your examples I would have used that rather than which. And I concur with Henri as regards the use of the comma.

But I'd also like to show how the reading of the examples changes based on the presence of the comma:

1. In reverse manner, a problem relating to pride, which challenges our life, is a magnified sense of inadequacy...

2. I remember an incident in my life, which lifted anger and wrath to new heights.

3. ...Our system is comprised of two units, which work together.

In the first example, the placement of the comma before which actually highlights the confusing message of the sentence. Is it pride that the phrase modifies, or does it point back to the subject, problem...? The sentence could be rewritten to make the statement more understandable and less questionable.

In the second example, again, the placement of the comma underscores the potentially unclear message. Does the author mean that the act of remembering becomes the catalyst for the present anger? Or was the author recalling an angry moment that followed a specific incident? Probably, the author means to say that the incident itself became an immediate impetus for personal feelings of anger, in which case adding the comma would lead to further confusion.

In the third example, the comma neither clarifies nor obfuscates. The verb work clearly ties back to units (rather than system).

As to your points, I can see now how the commas change the meaning of the sentence. I also see how, given you have not read those chapters 1,000 times, you would have no idea what they are about, and yet you grasped the meaning very well. This pleases me somewhat.

As to sentence 1 - The writer was discussing how pride changes one's behaviour. In this paragraph, she is contrasting that with one who constantly says, "I'm not good enough," and yet they are at the top of their game. I think the use of the commas clarifies the sentence better for me. Though, I think I will give this some thought.

In sentence 2, Tim, you hit the nail on the head when you said, "Probably, the author means to say that the incident itself became an immediate impetus for personal feelings of anger." This was an introduction to an example of how she allowed anger to color her reaction to individuals. I will leave off the commas in this case.

In sentence 3, this is yet another example of a particular point. The point of this example is that her 2 units, one outdoors and one in the attic, must work together to provide air-conditioning to the house. Both units must then be wired to a thermostat, or neither will work. So when Henri said, "I don't regard the fact that they work together essential for identifying them," their working together is in fact the essential part of this example.

scw1217 wrote:... So when Henri said, "I don't regard the fact that they work together essential for identifying them," their working together is in fact the essential part of this example. ...

That they work together is indeed, as you say, scw1217, that which makes the comparison with «faith, hope and love» meaningful. Still, as the system comprises only these two units, I shouldn't regard this information necessary for the purpose of syntactical identification, and should therefore consider the following relative clause as restrictive, and thus to be set off with a comma. If one wished to make the comparison with faith, hope, and charity clearer still, one could rephrase the sentence : «Our system comprises two units which must work together, in order to function.»...